The rise in US maternal mortality: the cause will surprise you

Mother Headstone

Recently, two important papers were published that shed a great deal of light on a previously murky topic, the US maternal mortality rate.

Up to this point the observed increase in maternal mortality has been difficult to parse because the new US death certificate, redesigned to capture more instances of maternal death, was only gradually adopted by the states. Is the observed incidence real or simply the result of better record keeping? A superb analysis by MacDorman et al. makes it clear that the increase is real,  albeit only a fraction of the apparent rise.

[pullquote align=”right” cite=”” link=”” color=”” class=”” size=””]The women most in need of highly technological medical care are failing to get it.[/pullquote]

But, as another study makes clear, the rise in US maternal mortality is NOT the result of poor medical practice or overuse of medical technology. Maternal mortality is closely tied to race and socio-economic status. Often the women most in need of highly technological medical care are failing to get it.

The MacDorman study is entitled Is the United States Maternal Mortality Rate Increasing? Disentangling trends from measurement issues.

Studies based on data from the 1980s and 1990s identified significant underreporting of maternal deaths… To improve ascertainment, a pregnancy question was added to the 2003 revision of the U.S. standard death certificate…

However, there were delays in states’ adoption of the revised death certificate … This created a situation where, in any given data year, some states were using the U.S. standard question, others were using questions incompatible with the U.S. standard, and still others had no pregnancy question on their death certificates.

Due in part to the difficulties in disentangling these effects, the United States has not published an official maternal mortality rate since 2007…

Now that the standard has been adopted in all states, the authors were able to correct the data to take into account previous underreporting during the years before an individual state adopted the revised death certificate standard.

What did they find?

Most of the observed increase in US maternal mortality can be ascribed to changes in the death certificate, but not all.

…[C]ombined data for 48 states and DC showed an increase in the estimated maternal mortality rate from 18.8 in 2000 to 23.8 in 2014 – a 26.6% increase.

The authors conclude:

Clearly at a time when WHO reports that 157 of 183 countries studied had decreases in maternal mortality between 2000 and 2013 (21), the U.S. maternal mortality rate is moving in the wrong direction. Among 31 Organization for Economic Cooperation and Development (OECD) countries reporting maternal mortality data, the U.S. would rank 30th, ahead of only Mexico.

Curiously the authors did not address perhaps the most pressing question about US rank. They’ve just shown that prior to the changes in the death certificate, the US failed to capture a substantial portion of maternal deaths. We were ranked higher internationally then because we weren’t providing accurate statistics. Yet the authors assume that maternal mortality rates in all other countries are accurate. Is that assumption justified? Have we fallen in international rankings simply because our maternal mortality statistic are more accurate than other countries? I’m not familiar enough with the individual maternal mortality assessments in other countries to answer that question, but perhaps they are.

The increase, however, is real and that is deeply troubling. What’s going on?

To answer that question, Amirhossein et al. compared maternal mortality rates by state in a just published study, Health Care Disparity and State-Specific Pregnancy-Related Mortality in the United States, 2005–2014.

They found tremendous variation in mortality rates between states.

…There was a significant correlation between state mortality ranking and the percentage of non-Hispanic black women in the delivery population. Cesarean deliveries, unintended births, unmarried status, percentage of non-Hispanic black deliveries, and four or less prenatal visits were significantly (P<.05) associated with increased maternal mortality ratio.

As the authors explain:

Although the United States has a higher rural population than many European nations, such factors are present to an even greater degree in Canada, which is even more rural, yet has a maternal mortality ratio of 10 per 100,000 live births.Furthermore, our data failed to identify a statistical correlation between statewide maternal mortality and either rural status or poverty.

Immigration has also been cited as a factor in this trend. However we found lower mortality for Hispanic women who make up the majority of recent immigrants…

The high U.S. cesarean delivery rate has also been invoked as an explanation for increased mortality, yet our data demonstrate only a weak correlation of mortality with cesarean delivery. Furthermore, previous work has demonstrated that this correlation does not reflect causation—the overwhelming majority of maternal deaths associated with cesarean delivery is a consequence of the indication for the cesarean delivery, not the operation itself.

Although medical factors such as hypertensive disease, diabetes, tobacco use, and obesity have been shown to be correlated with increased maternal morbidity, statewide population differences in rates of these conditions were not significantly correlated with mortality ratios.

Not surprisingly, the authors conclude:

First, states that may pride themselves on the intrinsic quality, leadership, organization, and funding of obstetric health care in their state based on national maternal mortality ratio rankings must realize that in many instances, such favorable rank simply reflects a different proportion of non-Hispanic black patients in the population rather than intrinsically superior medical care

Second, health care statistics that do not adjust for these important demographic factors are of little significance in judging the intrinsic quality of available health care in an individual state. Most importantly, these data strongly suggest that racial disparities in health care availability, access, or utilization by underserved populations are important issues faced by states in seeking to decrease maternal mortality. Ethnic genetic differences may also be involved. In addition, the potential role of unconscious (implicit) bias in this significant racial disparity must be considered. (my emphasis)

A startling example:

We note that although Washington, DC, has the highest maternal mortality ratio in the nation, non-Hispanic white patients in this district have the lowest mortality ratio in the United States. Excellent care is apparently available but is not reaching all the people.

These findings have important implications for international rankings that don’t adjust for demographic factors. The US has the highest proportion of non-Hispanic black women of any industrialized country. Our relatively poor ranking on maternal mortality may have little to do with the quality of US obstetric care and depend largely on access to it.

The rise in US maternal mortality may be much smaller than it originally appeared, but it is rising nonetheless and that calls for a vigorous response. We need to ensure that the women most likely to die from pregnancy related causes have access to the care that prevents maternal deaths.